WEDNESDAY, May 1, 2019 (HealthDay News) -- Multiple sclerosis, epilepsy and Parkinson's can be physically taxing conditions, but new research shows they exact a huge financial toll as well.

Over a 12-year period, out-of-pocket costs for Americans with these illnesses jumped, with the biggest increase seen among people with multiple sclerosis (MS). Those patients paid 20 times more for their drugs in 2016 than they did in 2004.

That means someone paying just $15 a month for medications in 2004 had to pay an average of $309 a month in 2016, the study findings showed.

Study author Dr. Brian Callaghan said that increase wasn't just for newer medications. He noted that both newer and older medications for MS all cost about the same.

"Out-of-pocket costs are mostly proportional to how expensive the drugs are," he said. Callaghan is an associate professor of neurology at the University of Michigan in Ann Arbor.

For example, the monthly out-of-pocket cost for epilepsy more than doubled, from $18 in 2004 to $40 in 2016, the researchers reported.

The study relied on information from a large, privately insured health care claims database. The researchers included data on more than 100,000 people with MS, more than 300,000 with peripheral neuropathy, over 280,000 with epilepsy, nearly 121,000 with dementia and almost 91,000 with Parkinson's disease.

Monthly out-of-pocket costs for those in high-deductible plans were twice as high compared to those with different insurance plans. In 2016, someone with MS and a high-deductible health insurance plan paid an average of $661 per month, compared to $246 a month for those who didn't have a high-deductible plan.

The total costs someone paid varied widely. The study found that 5% of people with MS paid just $90 for their medications in two years. But another 5% had to a pay nearly $10,000 for their medications.

Bari Talente, executive vice president of advocacy for the National Multiple Sclerosis Society, said affordability and access are two big problems facing people with MS.

"We're very fortunate to have more than a dozen disease-modifying medications, but from 2004 to 2016, there's been a tremendous increase in the list price of MS medications and a shift in the insurance markets to high-deductible health plans, with increasing deductibles and co-insurance. People with MS are getting hit from all sides," she said.

Talente said the average cost of medication for someone with MS was around $16,000 in 2004, and in 2016 was around $80,000.

"There's no way individuals and families can afford the current costs," she added.

"These costs are adding a lot of stress and anxiety to people's lives as they're trying to figure out how to live well with a chronic condition that can be exacerbated by stress. The disease can cause fatigue and cognitive [thinking] difficulties, making it even harder to navigate through a difficult system," Talente said.

Of the increase in out-of-pocket costs, Holly Campbell, deputy vice president of public affairs for PhRMA, a trade group representing pharmaceutical companies, said, "After discounts and rebates, medicine costs and prices are growing at the slowest rate in years."

But, Campbell said, "Too often these negotiated savings are not shared with patients, resulting in the sickest patients paying higher out-of-pocket costs to subsidize the healthy. This is the opposite of how health insurance is supposed to work. Health insurers are shifting more costs onto patients through deductibles, increased use of coinsurance, and the use of four or more tiers for prescription drugs."

But Talente stressed that a drug's original list price does matter. "In high-deductible plans, the price someone pays is often based on that list price," she explained.

Talente said the MS society recommends that the drug pricing process needs to be simple and transparent. If there are rebates, they should go back to the people paying for the drugs.

Callaghan said that patients and their doctors need to have a discussion about drug costs. Doctors have no way of knowing what each patient will be asked to pay at the pharmacy counter. So let your doctor know if you're having trouble paying for your medication.

It would also be ideal, he said, if doctors could know the actual cost a patient will be asked to pay when they're prescribing medication.